Surviving the Extremes: A Doctor's Journey to the Limits of Human Endurance (23 page)

To adapt to their extreme environment, however, desert animals
rely less on their physiology than on their behavior. The heat-stressed hypothalamus in mammals, while orchestrating a defensive response from blood vessels, sweat glands, and heat-shock proteins, is also signaling the cortex to go on the offensive, inducing behavior that can dramatically reduce heat load by modifying the surrounding microenvironment—from loosening clothing to seeking or creating shelter. No matter how complex the response, when this behavior is triggered at the subconscious level, we call it instinct. But if signals also reach the conscious mind and create the painful awareness of being “too hot,” then the animal or human will additionally be driven by the will to survive. Life-saving behavior for a species accustomed to modern technology might be as simple as a speedy retreat to an air-conditioned hotel, but in extreme environments, the links to civilization are easily broken. For the Hughes family, the break was as easy as getting lost on a desert road. For Mauro Prosperi, it took only one brief sandstorm to separate him from the elaborate artificial contrivance of the desert marathon and plunge him into a far more natural, elemental world, an arena in which his life depended on the resilience of his body and the activation of his latent primitive instincts.

Prosperi was put on the same playing field of survival as every other desert animal. Like them, he had to reduce heat production and increase heat loss. Any physical activity consumes energy and generates heat; that cost has to be offset by longer-term benefits in energy conservation and heat dissipation. Moving into the shade is cost-efficient—it can lower the temperature by 20°F to 30°F—but that still may not provide enough protection, especially against the solar radiation reflected up from the much hotter dry surface sand. Prosperi was lucky to find not just shade but that shrine, whose floor insulated him from the sand and whose walls blocked the wind. The shrine provided the same shelter for him as it did for the bats.

Once a desert animal, especially a big mammal, is on the move, shade is hard to find. Camels, whose desert ancestry goes back millions of years, have developed a portable sun-blocking system called fur. Their mat of individual hairs deflects solar radiation while still allowing cooler air to circulate underneath and also leaving space for sweat to
evaporate. Prosperi did not have their adaptive advantage, but he did have a human invention that was designed for precisely the same purpose: a loose-fitting Lycra running suit.

Animals without good thermal protection, such as hyenas and snakes, deal with the heat problem by being nocturnal. Without low-light vision or infrared sensors, night travel would be dangerous for a human. Prosperi compromised. He walked in the early morning and late evening, resting during the heat of the day behind a bush, a rock, a dune—anything that would cast a shadow.

The lack of moisture in the air and sand means that the desert is unable to retain heat once the sun disappears. Ground temperature can vary over 100°F from day to night. One of the best energy investments a desert inhabitant or a human visitor can make is to dig a hole in the sand. At a depth of 6 feet, sand provides enough insulation to maintain a nearly constant temperature of 50°F to 60°F. Aardvarks, jerboas, and toads burrow into the sand to sleep; and so did Prosperi.

The extreme temperature fluctuations that forced the runner and the other animals underground also generate a daily supply of water, if you know how to collect it. Air, even desert air, always contains some moisture. Since cold air cannot hold as much moisture as hot air, the rapid, drastic drop in temperature at night causes what little water there is in the air to precipitate out. The water condenses on rocks and surface sand before being evaporated by the morning sun. Desert beetles know how to collect it. They face the cool morning breeze and raise their concave backs; water that condenses there trickles down into their mouths. Prosperi collected some of the condensed water by licking the morning dew from crevices and depressions in rocks. He would have done much better had he carried a large plastic sheet with a hole in the middle and placed it over a pit in the sand. Putting rocks around the edge of the plastic to prevent it from falling in, and adding one rock toward the center to weigh it down, he would have created a funnel to channel condensed water down the hole and into his water bottle positioned underneath. The desert is stingy; the overnight collection would not have given him enough to live on, but he could have added the drops to whatever else he found each day.

Prosperi didn’t have that technological advantage, so he was reduced
to trying to get water the same way desert animals do. Besides licking rocks, he pulled up any rare tuft of grass he came across and sucked on the roots. He followed wadis and, the day before his rescue, found one that still contained a small, muddy puddle. He drank like a camel and, like a camel, lay by his watering hole overnight.

What little water Prosperi found during his ordeal he recycled by drinking his own urine. This might seem like taking poison—and in some ways it is—but it helped prolong his survival. Salts in the urine never become as concentrated as they do in the blood. Putting the liquid back in the blood therefore results in relatively more water being added than salt, a net increase in fluid volume. Because the urine will contain a high concentration of urea—a toxin that will eventually damage the kidneys—it can only be drunk a little at a time. So while it might be okay to drink urine, it can very quickly become too much of a good thing.

That caution applies to food as well. Like any other carnivore, Prosperi tried to hunt, but he was lucky not to have been too successful, for while he may have had the same hunger drive as the animals around him, he didn’t share their metabolism. Animals as predators possess heat-resistant enzymes that digest other animals more efficiently and excrete the by-products with less water loss than humans do. Animals as prey have high fat and protein content; eating them requires more energy and gives off more heat than eating plants, which are mostly ready-to-digest carbohydrates. That’s the reason why human visitors to a hot climate eat less and often feel an instinctive aversion to meat and fats.

Humans can go a long time without food, and if they are without water, they should. Even digesting carbohydrates consumes water, and all foods contain at least some salt, which dries out the body even more. Travelers lost in the desert don’t die of hunger; they die of thirst as they wander around with no chance of finding their way out.

Mauro Prosperi was hopelessly lost in a wilderness with too much vacant space and too few landmarks. Yet navigation is not a problem for seabirds that can cross entire oceans following lines of magnetic
force. Adding insult to injury, it’s not even a problem for desert ants; their photoreceptors enable them to follow patterns of polarized light in the sky. Hapless humans, however, are oblivious to magnetism and polarization, and so, if we have neither a compass nor knowledge of stars, we’re clueless when it comes to large-scale navigation. Prosperi’s only hope for survival in the Sahara was to stumble across someone capable of rescuing him, and he did—that eight-year-old girl. The marathoning Italian policeman and the goat-herding Tuareg child stood on the same barren patch of sand at the same moment. Both were human beings, sharing roughly the same physiognomy. Yet the little girl was thriving, while the marathon man was dying. The difference in their well-being at that moment was a result less of adaptations in their bodies than in their brains. Over the centuries, Tuaregs have learned how to traverse the desert by carrying simple tools, following basic landmarks, and knowing where to find water and shelter. At first, Prosperi’s desert crossing was no different. He carried a backpack, followed a marked trail, and knew that there would be water and tents at every checkpoint. But he was guided by the rules contained in his race manual. Tuaregs are guided by the teachings of their elders. Prosperi’s existence was dependent on the Marathon des Sables—a thin artificial culture temporarily laid over the desert. One brief sandstorm blew away that net of support. Once exposed to the elements, he was barely able to survive nine days. Tuaregs have thrived in the same environment for generations because their deeply rooted culture arises naturally from their surroundings, making it much less vulnerable to the vicissitudes of the desert. Pushed to the limits of survival, both will resort to inbred animal instincts. Tuaregs, however, have many more layers of protection before being forced to that level, and they all originate in the mind.

Humans in the desert are physically challenged compared with their animal neighbors: they’re too sensitive to heat, they can’t store enough water, have limited endurance, and can’t tune in to natural navigation systems. They do possess, however, a supreme capacity to learn by observation, to store and transmit information using language, and to integrate and apply their knowledge by turning survival
skills into customs. In other words, they overcome their handicaps with their brains.

Desert people have learned to mimic the anatomy of the other large but far more adept (and adapted) desert mammal, the camel. Lacking adequate fur, nomads cover themselves completely in loose-fitting robes,
jalabas,
which deflect sunlight, allow air to circulate, and leave space for evaporation. Born without the camel’s padded feet to insulate them from the hot desert sand, nomads cover their bare feet with knitted wool socks. Camels have dense hairs in their nostrils and ear canals, and a double set of long eyelashes to keep windblown sand out of their noses, ears, and eyes. Humans make up for their meager hair supply by wrapping their heads with shawls, leaving exposed only a narrow slit for their eyes. A camel’s nose has a large hollow chamber in which air is cooled before it is exhaled, allowing the water that condenses out to be recycled. Tuaregs sleep with scarves across their mouths to trap the moisture in exhaled air so that they can breathe it in again.

Even with all our adaptive ingenuity, a human’s performance in the desert falls far short of that of a camel, some of whose physical features simply cannot be replicated. A nomad can still profit from them, however, by domesticating the animal and exploiting its capabilities for his own ends. Camels are unequaled in their ability to survive passages across vast stretches of desert without water or shelter. Distant oases are reachable for nomads only because they have camels to bring them there. Camels store huge quantities of water. In a few hours they can drink 50 gallons, which they distribute not—as children are sometimes told—in their humps or any other specific place but all over their bodies. This water is not accessible to humans, but it does keep the camel going a long time, turning it into a mobile carrier on which can be hung gourds filled with water that
is
quite accessible.

Camels are also portable shelters. They are large but narrow-chested animals that, if given the choice, will orient themselves parallel to the sun’s rays to minimize radiation absorption. If the beasts are led perpendicular to the sun’s rays, however, nomads can walk continuously in their broad shadows. The bulk of a camel’s body is supported several feet off the ground on long thin legs—an evolutionary trait
that minimizes contact with the layer of air immediately above the sand, which is superheated during the day and supercooled at night. Temperatures 6 or 8 feet off the ground are far more moderate. With a camel to ride atop during the day and to use as a sleeping platform at night, any nomad will be ensured a more pleasant journey.

Still, the desert traveler and even the desert dweller live in constant fear of dying of thirst or of getting lost. They must fully exploit every advantage their brains can give them to minimize the risk. They must make utmost use of their power to plan ahead and their capacity to remember the distant past. On journeys when they have water to spare, nomads might collect ostrich eggshells, fill them with water, and bury them along the route, knowing that the next time they pass this way they could be desperately thirsty and that the prepositioned caches might save their lives. The water won’t be useful, however, if it can’t be found. Nomads can’t detect magnetic fields or sense polarized light like birds or ants, but they can see paths through the desert using maps that exist only in their minds. They can recognize subtle landmarks they have never seen before that will guide them to places they have never been. They have internalized the instructions passed down to them by previous generations, and so are able to follow the invisible tracks left by their ancestors.

These adaptations are uniquely human, although nomads share many other behavior patterns with their desert cohabitants. Some of the duplication is the result of learning to imitate animals’ survival methods, but much of it is generated by a common instinct that transcends individual species. Responding to the same environmental threat, animals and humans are pushed to develop the same strategies to defeat it, but humans often go one better. All desert creatures look for water along dried-up wadis. Kalahari bushmen, however, know that even when wadi grass roots are dry, they should be buried in a hole in the warm sand to generate a little moisture. It can then be sucked up through a hollow reed inserted into the hole. There may also be some water to extract from grassless wadis. Current slows at every bend in a river, especially around its outside curve. Some of the water that collects at these bends will percolate down into the sand and may remain there long after the surface has dried up. Digging up
the subsurface sand along an outer bend, then placing it in a cloth and squeezing it, may yield a few precious drops of water.

Chasing food is often a losing proposition in the desert. The pursuit generates heat, and the prize may not provide as much energy as was lost catching it. Most desert predators limit their chases to short sprints. Nomads never run at all. They catch some prey by setting traps, but mainly keep their meat supply close at hand by traveling with goats and sheep. The prized desert dessert is a date. It’s the perfect hot weather food, 70 percent carbohydrates and the rest water. Animals and humans alike are attracted to them. Animals lucky enough to come upon a date-palm oasis will eat their fill, and so will humans, who will then pack more to take along on their journey. And before leaving, they will replant some of the seeds to provide more “luck” for next time.